Measurement setup (1. . . mechanic design, 2. . . sensors, 3. . . actuators, 4. . . amplifying circuits,
5. . . break out box analog and digital signals, 6. . . data acquisition card, 7. . . embedded pc)
Real-time Linux based low cost rheometer
Rheologic measurement cycles do take a certain amount of time and the number of rheometer-devices is limited, therefore it is often not possible to carry out a large test series. It is intended to raise the amount of control samples in quality assurance and laboratory environments with new automated low cost measurement devices. A low cost principle which should be accomplished by a new measurement concept, usage of low cost parts and open source products in control system design has been built. It is optimized for Bitumen (remains of distillation of crude oil with a colloidal structure) which changes viscosity typically in a range of 107 but it can nevertheless be used for many other materials as well. Results of the material property analysis have been presented at the conference on visco-plastic fluids in Rio de Janeiro, Brazil (VPF2011).
Most real-time applications in context of automatic control and data acquisition do require user interfaces to change parameters or to extract data at runtime. Especially in prototyping control processes, it is common to use CACSD programs such as Matlab or Scicos for code generation. While still being in the prototyping stage the customer demands to start the evaluation of the prototype using a software tool. Very often those customers do not possess the ability to work with CACSD tools or other tools such as xRTAILab because of missing licenses or the lack of knowledge in linux. To close the gap between the real-time target and data evaluation, a remote control framework is introduced. The approach discussed in this work is to use RTAIXML (Figure 1) as a XML-RPC server. It is running on the rt-system and has the ability to connect to the CACSD generated code. This server instance can be contacted through a platform independent Java framework which allows quick prototyping of simple to use user interfaces without interfering the control system development. It is possible to transfer scopes and to change parameters on running targets.
Continuing the thesis work of Daniel Schleicher and Klaus Oppermann two existing rheometers (Figure 2) have been merged. The embedded system platform was equipped with a new real time platform and new control targets. Furthermore the amplifying hardware has been adapted to work together. On top of the embedded system a new, already mentioned, remote control framework was developed (which has been presented at the real time linux conference RTLWS2011 in Prague and was successfully applied in an end user application. Last but not least, a small set of tests was carried out with the now fully operational prototype and compared with professional equipment from Anton Paar GmbH.
Keywords: bitumen, rheometer, visco-plastic materials, real-time Linux, Java, webservice
Figure 2 : Schematic - Realtime application interface
November 16, 2011